LTPP study drives new Austroads report

One of the most important studies of long-term pavement performance ever undertaken is set to provide an important new legacy for Australian roads.

ARRB’s overall long-term pavement performance (LTPP) study, undertaken by Dr Tim Martin and Lith Choummanivong over a 24-year period, will live on through a new Austroads project.

The project (AAM6214) is aimed at updating the road deterioration (RD) models published by Austroads in 2010 using the additional 10 years of LTPP and LTPP Maintenance (LTPPM) observational data. This update will also include the LTPP data that is available from Australian and New Zealand road agencies.

Dr Martin will continue this work in his new role as ARRB’s National Discipline Leader for Performance Modelling in ARRB’s Road Asset Performance team.

He is focused on providing technical expertise on performance modelling and knowledge transfer of this to ARRB’s younger professionals. Dr Martin has a long history in this work, based on a strong passion for understanding its drivers.

Pavement performance in the form of pavement deterioration and works effects modelling is an essential part of any Pavement Management System (PMS). This type of modelling assists with estimating long-term maintenance investment requirements and the consequences on future pavement condition due to annual budget allocations for maintenance treatments on road segments.

Studying how roads perform in Australia’s unique combination of extreme weather, heavy vehicle traffic conditions, where the gross vehicle mass can be more than 150 tonnes, and sheer size of the road network, has been the focus of Dr Martin and Mr Choummanivong’s LTPP study, which began in 1994.

Dr. Tim Martin and ARRB alumni, Lith Choummanivong, with an ARRB survey vehicle

After reporting annually on their findings, a final report of this overall long-term pavement performance (LTPP) study, was published in 2019.

Based on the evidence of this study, it will leave a legacy ranging from a better understanding of how to prolong the life of our roads by making them more durable through sound management to give reduced whole of life-cycle costs.

The duo’s mission was to understand and predict how roads deteriorate using various surface maintenance treatments under the impact of heavy vehicle traffic loads and weather conditions where temperatures range from blazing heat to below zero. They studied 79 individual segments of road throughout Queensland, NSW, the ACT, Victoria, Tasmania and South Australia as part of their LTPP study.

“Previous work in this area had been done in Brazil, Kenya and South Africa, but not for our road conditions,” Dr Martin says.

“Now we’ve built road deterioration (RD) models and works effects (WE) models for the impact of maintenance for arterial roads in Australia, and they are uniquely Australian.”

Based on data collected between 1998 and 2018 from eight LTPPM sites, with a total of 40 individual road segments, this part of the study investigated the influence of maintenance and surface treatments on pavement performance. According to the report, the progression rate of each observed distress – deflection, roughness, rutting and cracking – was used as a performance indicator.

The results showed that the periodic maintenance treatments such as geotextile reseals and polymer modified binder (PMB) reseals significantly reduce the rate of pavement deterioration in terms of roughness, rutting and cracking as expected. There was only a marginal reduction in pavement deterioration with normal reseal treatments.

As a result of the project, the study team documented the outcomes of other studies on the development of an asphalt and seal life prediction model based on bitumen hardening from more than 257 asphalt and 124 seal samples collected across the country.

The study developed interim WE models for a wide range of surface treatments as well as interim network-level functional and structural RD models for flexible pavements. These models, along with WE models, were adapted into the PMS used by the New South Wales, Victorian and Western Australian road agencies.

One of the other primary outcomes of the study, according to Dr Martin, is the observations made around the impact of heavy vehicles on long-term pavement performance. By understanding the impact heavy vehicles have on the maintenance and performance of roads, Dr Martin says it can influence a key asset management element such as heavy vehicle road charging.

Using this information, he explains, can help road agencies create long-term strategies for cost savings and for implementing road user charging models with definitive estimates of road wear costs that vary with traffic levels, pavement strength and climate so that the user charging is accurate and justified.

“A flexible heavy vehicle charging system is something that has to happen, and one of the long-term views is that we'll move to electric vehicles, which won't have a fuel excise. So, we need to investigate these options, and the results of the study can help bring that about.”

An interesting observation Dr Martin notes as part of the study was the period in the early 2000s where there were a number of years that experienced less-than-average rainfall. “What we found was that the roads actually got stronger and the climate really benefitted their strength. Climate is a big variable and can affect the road in many ways – it was just a very unusual thing to observe,” he says.

Looking ahead, Dr Martin says the next steps for the learnings and models produced from the study is to continue to communicate their benefits to the industry.

This work is already world-renowned, and has won two Best Paper Awards at North America’s world-renowned International Conference for Managing Pavement Assets (ICMPA).

Contemporaries say it may be the most accurate and reliable study of its kind ever produced.

This work can be found on the Austroads website.

For more information, please contact our Road Asset Performance team here.